The operating speeds of semiconductor devices have continued to increase and continuously push the limit of conventional packaging technology.
To support the ever increasing operation speed of semiconductor devices, a differential pair is often used. A differential pair is a pair of conductors used for differential signaling. A differential pair reduces crosstalk and electromagnetic interference and can provide constant and/or known characteristic impedance. Furthermore, a differential pair enables impedance matching techniques used for high-speed signal transmission lines. Non-limiting examples of a differential pair include twisted-pair, microstrip and stripline.
A differential pair reduces the total current between the two conductors of the differential pair, as Kirchhoffs Law predicts the total current as being zero through a cross section of the differential pair. The condition for emitting zero electromagnetic interference representing zero crosstalk is for zero total current through the cross section of the differential pair. However, in real world situations, zero current is not achieved, resulting in crosstalk between the conductors of a differential pair.
Additionally, crosstalk may occur between differential pairs as a result of second-order effects due to the finite impedance of the current source and impedance mismatch between the devices. For this case, the two conductors of the differential pair may be considered as a dipole with coupling on the order of l/r2 or l/r4, where r is the distance between lines of differential pairs. To reduce crosstalk, the effects associated with second-order effects need to be reduced.
The differential to differential pair crosstalk in electronic equipment limits its applicability to higher than 5 GHz types of Serializer/Deserializer (Serdes) designs. The crosstalk between differential pairs needs to be kept to a level of around −60 dB or less in order to minimize its impact on the channels ability to receive a greatly attenuated signal.
Modem signal channels at high speed can introduce an attenuation of 40 dB or more. To properly receive such a signal in the presence of a fully duplexed communication stream, a cross-coupling immunity of 60 dB is needed for reliable signal reception.
The crosstalk between differential pairs can be calculated.
In order to determine the crosstalk between differential pairs, the mutual inductance is calculated. The mutual inductance by a filamentary circuit i on another filamentary (consisting of wires and rods) circuit is given by the double integral Neumann formula as give by Equation 1 below:
                              M          ij                =                                            μ              0                                                      4                ⁢                                                                  ⁢                π                            ⁢                                                                            ⁢                                    ∮                              C                i                                      ⁢                                          ∮                                  C                  j                                            ⁢                                                                    ds                    i                                    ·                                      ds                    j                                                                                                          R                    ij                                                                                                                            (        1        )            
Where μ0 denotes the magnetic constant (4π×10−7 H/m), Ci and Cj are the curves spanned by the wires, Rij is the distance between two points.
The currents associated with the positive and negative conductors of a differential have the same magnitude of current but traversing in opposing directions.
Differential pair to differential pair crosstalk is a technology limiter that causes system failure in the form of signal detection error—increasing the system jitter and causing the signal detection eye pattern to close. An eye pattern, also known as an eye diagram, is a presentation (e.g. oscilloscope display) of a digital data signal as received at a receiver. Furthermore, the received signal is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep.
Reduction of this crosstalk is possible using a technique known as orthogonal crossovers. The use of crossovers between differential pairs introduces significant discontinuities in the transmission lines that make up the differential pairs. A significant source of the discontinuities are a result of the vias that are used to move the pair from one side to the other. A via in an integrated circuit or printed circuit board is a mechanism for transferring a signal from one signal layer to another signal layer.
Alternate methods used to reduce the reflections from the crossovers include designing the via structure in such a way as to match the characteristic impedance of the line.
FIGS. 1A-C illustrates an example conventional transmission line system 100.
Transmission line system 100 includes a differential pair 102 and a differential pair 104.
Non-limiting examples of a differential pair include twisted-pair, microstrip and stripline. Differential pairs 102 and 104 provide a transmission medium for transferring an electrical signal. A differential pair reduces crosstalk and electromagnetic interference and can provide constant and/or known characteristic impedance. Furthermore, a differential pair enables impedance matching techniques used for high-speed signal transmission lines.
Differential pair 102 includes a positive signal trace 106 and a negative signal trace 108. Differential pair 104 includes a positive signal trace 110 and a negative signal trace 112. In some embodiments, the positive signal associated with positive signal trace 106 is equal and opposite to the negative signal associated with negative signal trace 108. In other embodiments, the positive signal associated with positive signal trace 106 is different in magnitude to the negative signal associated with negative signal trace 108. In theory, for embodiments with equal but opposite signals associated with positive signal trace 106 and negative signal trace 108, the radiant electromagnetic field generated by the positive signal in positive signal trace 106 is cancelled by the equal and opposite radiant electromagnetic field generated by the negative signal in negative signal trace 108. Similarly, for some embodiments, the positive signal in positive signal trace 110 is equal and opposite to the negative signal in negative signal trace 112. In theory, radiant electromagnetic field generated by the positive signal in positive signal trace 110 is cancelled by the equal and opposite radiant electromagnetic field generated by the negative signal in negative signal trace 112.
The radiant effects of current through a differential pair may negatively affect the signals in an adjacent (or nearby) differential pair. In particular, a current traveling through one signal trace (or path) may affect the current traveling through another signal trace, wherein the magnitude is a function of distance. For example, current traveling through positive signal trace 106 will affect current traveling through positive signal trace 110, and will also affect current traveling through negative signal trace 112, but by a slightly less amount. Further, current traveling through negative signal trace 108 will affect current traveling through positive signal trace 110, and will also affect current traveling through negative signal trace 112, but by a slightly less amount. The overall effect is known as crosstalk interference, or crosstalk.
The total effects of crosstalk may be determined by integrating the effect along a length of the crosstalk, in this instance a length 114 noted as L. To simplify the discussion, first consider the effects of positive signal trace 106 and negative signal trace 108 on positive signal trace 110. Then, consider the effects of positive signal trace 106 and negative signal trace 108 on negative signal trace 112. This will be further described with reference to FIGS. 1B-C.
FIG. 1B takes into account the effects of currents of positive signal trace 106 and negative signal trace 108, as felt by positive signal trace 110. In this example, negative signal trace 108 and is separated from positive signal trace 110 by a distance 116 noted as r1, whereas positive signal trace 106 and is separated from positive signal trace 110 by a distance 118 noted as r2. The radiant effects of currents of positive signal trace 106, as felt by positive signal trace 110, are opposite to the radiant effects of currents of negative signal trace 108, as felt by positive signal trace 110. However, distance 116 is smaller than distance 118. Accordingly, the radiant effects of currents of negative signal trace 108, as felt by positive signal trace 110 are greater than the radiant effects of currents of positive signal trace 106.
FIG. 1C takes into account the effects of currents of positive signal trace 106 and negative signal trace 108, as felt by negative signal trace 112. In this example, negative signal trace 108 and is separated from negative signal trace 112 by distance 118 (again noted as r2), whereas positive signal trace 106 and is separated from negative signal trace 112 by a distance 120 noted as r3. The radiant effects of currents of positive signal trace 106, as felt by negative signal trace 112, are opposite to the radiant effects of currents of negative signal trace 108, as felt by negative signal trace 112. However, distance 118 is smaller than distance 120. Accordingly, the radiant effects of currents of negative signal trace 108, as felt by negative signal trace 112 are greater than the radiant effects of currents of positive signal trace 106 as felt by negative signal trace 112.
Comparing the situations illustrated in FIGS. 1B-C, it is clear that the radiant effects of currents of positive signal trace 106 as felt by positive signal trace 110 (as shown in FIG. 1B) is equal and opposite to the radiant effects of currents of negative signal trace 108 as felt by negative signal trace 112 (as shown in FIG. 1C). Accordingly, the radiant effects effectively cancel.
The remaining radiant effects are therefore drawn to the radiant effect of current of negative signal trace 108 as felt by positive signal trace 110 (as shown in FIG. 1B) in addition to the radiant effect of current of positive signal trace 106 as felt by negative signal trace 112 (as shown in FIG. 1C). Ideally, the current in positive signal trace 110 should be equal and opposite to the current in negative signal trace 112. However, radiant effect of current of negative signal trace 108 alter the current in positive signal trace 110, whereas the radiant effect of current of positive signal trace 106 will alter the negative signal trace 112. For simplicity of explanation, let the “alteration” the current in positive signal trace 110 be an attenuation, and let of the “alteration” the current in positive signal trace 110 additionally be an attenuation. The attenuation of the signal in negative signal trace 112 is less than the attenuation of the signal in positive signal trace 110 because r2<r3. The difference in interference creates a distortion in the signal if positive signal trace 110 and negative signal trace 112 are attenuated differently. Even though the interference may be minor, the interference calculation is integrated over the length of distance 114 or L as described by Equation 1.
In order to reduce crosstalk, conventional systems cross or switch conductors of a differential pair in order to balance the coupling between the differential pairs which will be further discussed with reference to FIG. 2.
FIG. 2 illustrates an example conventional transmission line system 200, wherein one set of signal traces include a crossover.
As shown in the figure, prior to a crossover point 206, positive signal trace 110 is separated from negative signal trace 108 by distance 116 (indicated by r1), whereas negative signal trace 112 is separated from positive signal trace 106 by distance 120 (indicated by r3). After crossover point 206, negative signal trace 112 is separated from negative signal trace 108 by distance 116 (indicated by r1), whereas positive signal trace 110 is separated from positive signal trace 106 by distance 120 (indicated by r3). For purposes of discussion, let crossover point 206 be in the middle of distance L.
The radiant effects of the current of negative signal trace 108 as felt by positive signal trace 110 from the left of the figure to crossover point 206 is equal in magnitude and opposite in sign to the radiant effects of the current of negative signal trace 108 as felt by negative signal trace 112 crossover point 206 to the right of the figure. Accordingly, the radiant effects of the current from the left side of the figure to the right side of the figure cancel each other out. Similarly, the radiant effects of the current of positive signal trace 106 as felt by negative signal trace 112 from the left of the figure to crossover point 206 is equal in magnitude and opposite in sign to the radiant effects of current of positive signal trace 106 as felt by positive signal trace 110 crossover point 206 to the right of the figure. Accordingly, the radiant effects of the current from the left side of the figure to the right side of the figure cancel each other out. Canceling the radiant effects is the purpose or goal of performing the crossover in differential pairs. Conventionally, crossovers are formed by “tunneling” below one of the signal traces.
Similar to performing crossovers with differential pairs, crossovers may be performed with bond wires as discussed with respect to FIGS. 3A-5D.
Crosstalk interference may additionally originate from other portions of a semiconductor device, namely bond wires.
A common semiconductor component encapsulates a semiconductor device in a package and uses bond wires to form a connection between the bond pads associated with the semiconductor device and the bond pads associated with the package. Bond wires may be adhered or welded to bond pads using some combination of heat, pressure and ultrasonic energy.
In a wirebond design the bond wire pair to bond wire pair coupling ranges from −17 dB to −38 dB for a range of spacing from 1(K) microns to 550 microns between the pairs. For a multi-channel Serdes link, the pairs need to be spaced at 600 microns or closer to get a reasonable number of channels into a given design. This is generally the case for wirebond designs, as wirebond designs are typically limited to 25 high speed input/output signal connections.
The standard solution for reducing bond wire to bond wire coupling is to space the pairs further and further apart. However, today's modem semiconductor die designs with large numbers of high speed input/output signals do not provide enough space to support −60 dB coupling.
Aspects of the conventional technology for bond wires associated with semiconductor packaging will now be described in greater detail with reference to FIGS. 3A-5D.
FIG. 3A illustrates a conventional bond wire configuration associated with a semiconductor device and a package.
A bond wire configuration 300 includes a semiconductor device 302, a package 304, a differential pair 305 and a differential pair 306. Differential pair 305 includes a bond wire 307 and a bond wire 308. Differential pair 306 includes a bond wire 310 and a bond wire 312. Semiconductor device 302 includes a bond pad 314, a bond pad 316, a bond pad 318 and a bond pad 320. Package 304 includes a bond pad 322, a bond pad 324, a bond pad 326 and a bond pad 328.
A signal (or power) line (not shown) on bond pad 314 connects to a corresponding signal (or power) line (not shown) on bond pad 322 via bond wire 307. A signal (or power) line (not shown) on bond pad 316 connects to a signal (or power) line (not shown) on bond pad 324 via bond wire 308. A signal (or power) line (not shown) on bond pad 318 connects to a signal (or power) line (not shown) on bond pad 326 via bond wire 310. A signal (or power) line (not shown) on bond pad 320 connects to a signal (or power) line (not shown) on bond pad 328 via bond wire 312.
Semiconductor device 302 provides electrical circuitry for electrical operations. Non-limiting examples for semiconductor device 302 include microprocessor and memory. Package 304 provides carriage and protection for semiconductor device 302. Differential pair 305 provides a transmission medium for transferring an electrical signal. Differential pair 306 provides a transmission medium for transferring an electrical signal. Bond pad 314. 316, 318 and 320 provide electrical connection to circuitry associated with semiconductor device 302. Bond pad 322, 324, 326 and bond pad 328 provide electrical connection to leads associated with package 304. As a non-limiting example, leads may be surface mount capable.
In operation, electrical signals traverse from semiconductor device 302 to bond pads 314, 316, 318, and 320. Furthermore, electrical signals traverse from bond pads 314, 316, 318 and 320 to bond pad 322, 324, 326, and 328 via bond wire 307, 308, 310 and 312, respectively. Furthermore, electrical signals traverse from bond pad 322, 324, 326 and 328 to electrical leads. Furthermore, electrical signals traverse from electrical leads to other electrical and electronic devices located external to package 304. Furthermore, crosstalk may occur between the bond wires and cause signaling errors. Crosstalk is a phenomenon by which a signal transmitted on one circuit or channel creates an unwanted effect in another circuit or channel. Crosstalk is typically caused by unwanted capacitive, inductive or conductive coupling from one circuit, part of a circuit or channel, to another. In general, the closer in distance channels are collocated, the greater the chance of experiencing crosstalk and conversely, the further the channels are collocated, the smaller the chance of experiencing crosstalk.
As an example, the separation between bond wire 307 and bond wire 308 and between bond wire 310 and bond wire 312 at semiconductor device 302 is configured for 70 microns. Furthermore, the separation between bond wire 307 and bond wire 308 and between bond wire 310 and bond wire 312 at package 304 is 100) microns. Furthermore, the distance between bond wire 307 and bond wire 312 at semiconductor device 302 is configured for 400 microns. Furthermore, the distance between bond wire 307 and bond wire 312 at package 304 is 400 microns. Furthermore, the distance between bond wire 308 and bond wire 310 at semiconductor device 302 is 70 microns.
In order to reduce issues associated with crosstalk, the separation between bond wires may be increased as will be discussed with reference to FIG. 3B.
FIG. 3B illustrates a conventional bond wire configuration associated with a semiconductor device and a package where bond wire separation is increased over the separation depicted in FIG. 3A.
As shown in FIG. 3B (and similar to the situation of FIG. 3A), the separation between bond wire 307 and bond wire 308 at semiconductor device 302 remains 70 microns and the separation between bond wire 307 and 308 at package 304 remains 100 microns.
However, as shown in FIG. 3B, the separation between bond wire 307 and bond wire 312 at semiconductor device 302 is 310 microns. This is a 90 micron decrease (22.5%) in distance of the similar separation of FIG. 3A. As shown in FIG. 3B (similar to the situation of FIG. 3A), the separation between bond wire 307 and bond wire 312 at package 304 is 400 microns. The separation between bond wire 308 and bond wire 310 at semiconductor device 302 is 170 microns. This is a 100 micron increase (142%) in distance of the similar separation of FIG. 3A. As shown in FIG. 3B, the separation between bond wire 308 and bond wire 310 at package 304 is 200 microns. This is a 100 micron (100%) increase in distance of the similar separation of FIG. 3A.
The increased separation of bond wires, as shown in FIG. 3B, provided less signal interference. As an example, the noise margin for the configuration as illustrated in FIG. 3B may experience a 10 dB improvement over FIG. 3A, as crosstalk is reduced due to the increased distance between bond wire 308 and bond wire 310.
FIG. 3C illustrates a conventional bond wire configuration associated with a semiconductor device and a package where bond wire separation is further increased over the separation depicted in FIG. 3B.
As shown in FIG. 3C (and similar to the situation of FIGS. 3A-B), the separation between bond wire 307 and bond wire 308 at semiconductor device 302 remains 70 microns and the separation between bond wire 307 and 308 at package 304 remains 100 microns.
As further shown in FIG. 3C, the separation between bond wire 307 and bond wire 312 at semiconductor device 302 is 410 microns. This is a 10 micron increase (2.5%) in distance of the similar separation of FIG. 3A and a 100 micron increase (32%) in distance of the similar separation of FIG. 3B. As shown in FIG. 3C, the separation between bond wire 307 and bond wire 312 at package 304 is 300 microns. This is a 100) micron increase (25%) in distance of the similar separation of FIGS. 3A-B. As shown in FIG. 3C, the separation between bond wire 308 and bond wire 310 at semiconductor device 302 is 270 microns. This is a 200 micron increase (285%) in distance of the similar separation of FIG. 3A and a 100 micron (58%) increase in distance of the similar separation of FIG. 3B. As shown in FIG. 3C, the separation between bond wire 308 and bond wire 310 at package 304 is 400 microns. This is a 300 micron increase (300%) in distance of the similar separation of FIG. 3A and a 200 micron increase (200%) in distance of the similar separation of FIG. 3B.
The noise margin for the configuration as illustrated in FIG. 3C may experience a 6 dB improvement over FIG. 38, as crosstalk is reduced due to the increased distance between bond wire 308 and bond wire 310.
In order to reduce issues associated with crosstalk, the separation between bond wires may be increased as will be discussed with reference to FIG. 3D.
FIG. 3D illustrates a conventional bond wire configuration associated with a semiconductor device and a package where bond wire separation is increased over the separation depicted in FIG. 3C.
As shown in FIG. 3D (and similar to the situation of FIGS. 3A-B), the separation between bond wire 307 and bond wire 308 at semiconductor device 302 remains 70 microns and the separation between bond wire 307 and 308 at package 304 remains 100 microns.
As further shown in FIG. 3D, the separation between bond wire 307 and bond wire 312 at semiconductor device 302 is 510 microns. This is a 110 micron increase (27.5%) in distance of the similar separation of FIG. 3A, a 200 micron increase (64.5%) in distance of the similar separation of FIG. 3B and a 100 micron increase (24.3%) in distance of the similar separation of FIG. 3C. As shown in FIG. 3D, the separation between bond wire 307 and bond wire 312 at package 304 is 600 microns. This is a 200 micron increase (50%) in distance of the similar separation of FIGS. 3A-B and a 100 micron increase (25%) in distance of the similar separation of FIG. 3C. The separation between bond wire 308 and bond wire 310 at semiconductor device 302 is 370 microns. This is a 300 micron increase (429%) in distance of the similar separation of FIG. 3A, a 200 micron (118%) increase in distance of the similar separation of FIG. 3B and a 100 micron (37%) increase in distance of the similar separation of FIG. 3C. As shown in FIG. 3D, the separation between bond wire 308 and bond wire 310 at package 304 is 400 microns. This is a 300 micron increase (300%) in distance of the similar separation of FIG. 3A, a 200 micron increase (200%) in distance of the similar separation of FIG. 3B and the same distance of the similar separation of FIG. 3C.
As an example, the noise margin for the configuration as illustrated in FIG. 3C may experience a 5 dB improvement over FIG. 3C, as crosstalk is reduced due to the increased distance between bond wire 308 and bond wire 310.
Clearly, as described above with reference to FIGS. 3A-D, crosstalk may be minimized by increasing the spacing between bond wires. To minimize real estate on semiconductor device 302 package 304 bond wires should ideally be disposed as close to one another as possible. As such, an appropriate spacing between the bond wires must be determined.
Other bond wire configurations may be used in an attempt to reduce coupling. These include overlapping bond wires, as will be described with reference to FIGS. 4A-C
FIG. 4A illustrates a conventional overlapped bond wire configuration associated with a semiconductor device and a package.
A bond wire configuration 400 includes a semiconductor device 402, a package 404, a bond wire 407, a bond wire 408, a bond wire 410 and a bond wire 412. Semiconductor device 402 includes a bond pad 414, a bond pad 416, a bond pad 418 and a bond pad 420. Package 404 includes a bond pad 422, a bond pad 424, a bond pad 426 and a bond pad 428.
A signal (or power) line (not shown) on bond pad 414 connects to a signal (or power) line (not shown) on bond pad 422 via bond wire 407. A signal (or power) line (not shown) on bond pad 416 connects to a signal (or power) line (not shown) on bond pad 424 via bond wire 408. A signal (or power) line (not shown) on bond pad 418 connects to a signal (or power) line (not shown) on bond pad 426 via bond wire 410. Bond pad 420 connects to bond pad 428 via bond wire 412.
The separation between bond wire 407 and bond wire 408 and between bond wire 410 and bond wire 412 at semiconductor device 402 is configured for 0 microns. Similarly, the separation between bond wire 407 and bond wire 408 and between bond wire 410 and bond wire 412 at package 404 is 0 microns. The distance between bond wire 407 and bond wire 412 at semiconductor device 402 is configured for 140 microns. The distance between bond wire 407 and bond wire 412 at package 404 is 200 microns. Similarly, the distance between bond wire 408 and bond wire 410 at semiconductor device 402 is 140 microns and the distance between bond wire 408 and bond wire 410 at package 404 is 200 microns.
Semiconductor device 402 provides electrical circuitry for electrical operations. Non-limiting examples for semiconductor device 402 include microprocessor and memory. Package 404 provides carriage and protection for semiconductor device 402. Bond pad 414, 416, 418 and 420 provide electrical connection to circuitry associated with semiconductor device 402. Bond pad 422, 424, 426 and bond pad 428 provide electrical connection to leads associated with package 404. As a non-limiting example, leads may be surface mount capable.
In operation, electrical signals traverse from semiconductor device 402 to bond pads 414, 416, 418 and 420. Furthermore, electrical signals traverse from bond pads 414, 416, 418 and 420 to bond pad 422, 424, 426 and 428 via bond wire 407, 408, 410 and 412, respectively. Furthermore, electrical signals traverse from bond pad 422, 424, 426 and 428 to electrical leads. Furthermore, electrical signals traverse from electrical leads to other electrical and electronic devices located external to package 404. Furthermore, crosstalk may occur between the bond wires and cause signaling errors.
The inductive coupling between the pair of bond wires 407 and 408 and the pair of bond wires 410 and 412 is calculated as −16.76 dB.
Similar to differential pairs, as discussed above with reference to FIGS. 1-2, in order to reduce issues associated with crosstalk in bond wires, the separation between bond wires may be increased, as will be discussed with reference to FIG. 4B.
FIG. 4B illustrates a conventional overlapped bond wire configuration associated with a semiconductor device and a package where bond wire separation is increased over the separation depicted in FIG. 4A.
The separation between bond wire 407 and bond wire 408 at semiconductor device 402 remains 0 microns and the separation between bond wire 407 and 408 at package 404 remains 0 microns as described with reference to FIG. 4A.
The separation between bond wire 407 and bond wire 412 at semiconductor device 402 is 340 microns. This is a 200 micron increase (143%) in distance of the similar separation of FIG. 4A. As shown in FIG. 48, the separation between bond wire 407 and bond wire 412 at package 404 is 400 microns. This is a 200 micron increase (100%) in distance of the similar separation of FIG. 4A.
The inductive coupling between the pair of bond wires 407 and 408 and the pair of bond wires 410 and 412 is calculated as −27.21 dB, which is an improvement of −10.45 dB over the configuration of FIG. 4A. The increased separation between the bond wires increases the noise margin, decreases the coupling and decreases crosstalk.
In order to further reduce issues associated with crosstalk, the separation between bond wires may be further increased as will be discussed with reference to FIG. 4C.
FIG. 4C illustrates a conventional overlapped bond wire configuration associated with a semiconductor device and a package where bond wire separation is increased over the separation depicted in FIG. 4B.
The separation between bond wire 407 and bond wire 408 at semiconductor device 402 remains 0 microns and the separation between bond wire 407 and 408 at package 404 remains 0 microns as described with reference to FIG. 4A.
The separation between bond wire 407 and bond wire 412 at semiconductor device 402 is 540 microns. This is a 400) micron increase (285%) in distance of the similar separation of FIG. 4A and a 200 micron increase (58.8%) in distance of the similar separation of FIG. 4B. As shown in FIG. 4C, the separation between bond wire 407 and bond wire 412 at package 404 is 600 microns. This is a 400 micron increase (200%) in distance of the similar separation of FIG. 4A and a 200 micron increase (50%) in distance of the similar separation of FIG. 4B.
The inductive coupling between the pair of bond wires 407 and 408 and the pair of bond wires 410 and 412 pair is calculated as −32.13 dB, which is an improvement of −4.92 dB over the configuration of FIG. 4B. The increased separation between the bond wires increases the noise margin, decreases the coupling and decreases crosstalk.
FIG. 4C illustrates a conventional overlapped bond wire configuration associated with a semiconductor device and a package where bond wire separation is increased over the separation depicted in FIG. 4B resulting in increased noise margin and decreased crosstalk.
Clearly, as described above with reference to FIGS. 6A-C, crosstalk may be minimized by increasing the spacing between bond wires. To minimize real estate on semiconductor device 402 package 404 bond wires should ideally be disposed as close to one another as possible. As such, an appropriate spacing between the bond wires must be determined.
Similar to methods of reducing crosstalk for differential pairs as discussed above with reference to FIGS. 1-2, crosstalk originating from bond wires may be reduced with orthogonal crossovers. This will be discussed with reference to FIGS. 5A-D
FIG. 5A illustrates a conventional crossed bond wire configuration associated with a semiconductor device and a package.
A bond wire configuration 500 includes a semiconductor device 502, a package 504, a differential pair 505 and a differential pair 506. Differential pair SOS includes a bond wire 507 and a bond wire 508. Differential pair 506 includes a bond wire 510 and a bond wire 512. Semiconductor device 502 includes a plurality of bond pads to which one end of the respective bond wires are adhered to. Package 504 includes a plurality of bond pads to which one end of the respective bond wires are adhered to.
For this configuration, bond wire 507 crosses over and above bond wire 508, whereas bond wire 512 crosses over and above bond wire 510.
The separation between bond wire 507 and bond wire 512 at semiconductor device 502 is 210 microns. The separation between bond wire 508 and bond wire 510 at package 504 is 400 microns.
The inductive coupling between the pair of bond wires 507 and 508 and the pair of bond wires 510 and 512 is calculated as −18.79 dB.
The coupling between the bond wires is dependent upon the point of crossing between the bond wires and upon the orientation between the bond wires. A variety of crossing bond wire configurations will be described with reference to FIGS. 5B-D below which have a variety of coupling values.
FIG. 5B illustrates a conventional crossed bond wire configuration associated with a semiconductor device and a package where bond wire orientation is varied as compared to FIG. 5A.
As shown in FIG. 5B, the separation between the bond wires at semiconductor device 502 and at package 504 is the same as described with reference to FIG. 5A, however the height of the bond wires is varied slightly.
In FIG. 5B, the inductive coupling between the pair of bond wires 507 and 508 and the pair of bond wires 510 and 512 pair is calculated as −17.53 dB. Furthermore, the −17.53 dB coupling is 1.26 dB greater than the configuration described with reference to FIG. 5A even though the difference between FIG. 5A and FIG. 5B is related to the height of the bond wires and not the separation between the bond wires at the bond pads.
FIG. 5C illustrates another example conventional crossed bond wire configuration associated with a semiconductor device and a package.
As shown in FIG. 5C, the separation between the pair of bond wires 507 and 508 and the pair of bond wires 510 and 512 is increased as compared to FIGS. 5A-B. The separation between the pair of bond wires 507 and 512 at semiconductor device 502 has been increased to 240 microns. This is a 30 micron increase (14%) in distance of the similar separation of FIGS. 5A-B. As shown in FIG. 5C, the separation between bond wire 508 and bond wire 510 at package 504 remains 400 microns.
The inductive coupling between the pair of bond wires 507 and 508 and the pair of bond wires 510 and 512 is calculated as −24.54 dB. The −24.54 dB coupling is 5.75 dB less than FIG. 5A and is 7.01 dB less than FIG. 5B.
FIG. 5D illustrates another example conventional crossed bond wire configuration associated with a semiconductor device and a package.
The separation between bond wire 507 and bond wire 512 at semiconductor device 502 is 240 microns, the same as described with reference to FIG. 3C. The separation between bond wire 508 and bond wire 510 at package 504 is 400 microns. The 400 microns is an increase of 100 microns over the separation as described with reference to FIG. 3C.
In FIG. 3C, the larger separation is 500 microns, whereas here the larger separation is 400 microns—meaning a tighter overall bondwire pitch while the isolation has improved from −23 dB to −27 dB.
The inductive coupling between the pair of bond wires 507 and 508 and the pair of bond wires 510 and 512 is calculated as −26.47 dB. The −26.48 dB coupling is 1.93 dB less than FIG. 5C.
What is needed is a system and method for decreasing crosstalk associated with differential pairs and bond wires.